On the principles and advantages of LED lighting and application program.

- May 15, 2017 -

Lighting principle

LED light source LED is composed of Ⅲ-Ⅳ compounds, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP (phosphorus arsenide) and other semiconductor made of its core is PN junction. So it has the general P-N junction I-V characteristics, that is, forward conduction, reverse cut-off, breakdown characteristics. In addition, under certain conditions, it also has light-emitting characteristics. At the forward voltage, electrons are injected from the N region into the P region, and the holes are injected into the N region from the P region. A fraction of the minority carriers (minority) entering the other region recombines with the majority of carriers (polygons) and emits light.

Assuming that luminescence occurs in the P region, the injected electrons recombine directly with the valence band holes, or are first captured by the luminescent center and then recombined with the holes. In addition to this luminescent composite, some electrons are captured by non-luminescent centers (this center is near the middle of the conduction band and the tape), and then recombined with holes, each time the energy released is not visible and can not form visible light. The higher the ratio of the amount of luminescence to the amount of non-luminescent compound, the higher the photon efficiency. Since the recombination is glowing in the minority diffusion region, the light is generated only within a few μm of the PN junction.

The theory and practice show that the peak wavelength λ of the light is related to the bandgap Eg of the semiconductor material in the light emitting region, that is, λ ≈ 1240 / Eg (mm)

Where Eg is the unit of electron volts (eV). If the visible light (wavelength of 380nm purple ~ 780nm red light), the semiconductor material Eg should be between 3.26 ~ 1.63eV. The light longer than the red light is infrared light. There are infrared, red, yellow, green and blue light-emitting diodes, but the Blu-ray diode cost, the price is very high, the use is not common.

Long life: LED light source it is called longevity lamp, meaning never turn off the lights. Solid cold light source, epoxy resin package, the lamp body is not loose part, there is no filament light burning, heat deposition, light failure and other shortcomings, the service life of up to 60,000 to 100,000 hours, 10 times longer than the traditional light source life the above.

More changes: LED light source can use red, green and blue three primary colors principle, under the control of computer technology to make three colors with 256 gray and arbitrary mixing, can produce 256 × 256 × 256 = 16777216 kinds of colors, the formation of different light Color combinations of changeable, to achieve a variety of dynamic changes in the effect and a variety of images.

Environmental protection: environmental protection is better, the spectrum is not ultraviolet and infrared, neither heat nor radiation, and waste can be recycled, no pollution does not contain mercury elements, cold light source, you can safely touch, is a typical green lighting.

LEDs need a completely different type of drive from incandescent or halogen. The incandescent lamp behaves as a purely resistive load with self-stabilizing characteristics, and LED requires a current source. The luminous flux produced by the LED is approximately proportional to the current flowing through the device. The forward voltage of the LED increases with increasing current, but decreases with increasing temperature. In this regard, LED behaves like a diode. However, the forward voltage (VF) of the LED during operation is large. This voltage is related to the energy (eV) generated when electrons are converted to photons, which are directly related to the color of light. In addition, the VF values between different production lots can vary widely.

Serial / parallel configuration

In most applications where LEDs are used to replace existing light sources, multiple LEDs are required to connect to the drive because a single LED can not produce enough light flux. LEDs can be connected in serial or parallel.

If the LED is connected via a serial connection, the total voltage on the LED chain is equal to the sum of the forward voltages (equal to the current on all LEDs).

If the LEDs are connected in parallel, the current will be distributed to each branch. However, since the forward voltage of an LED drops as the temperature rises, the configuration is inherently unstable. As the temperature rises, more and more current will flow to the branch with lower forward voltage, these branches will become brighter, and those with higher forward voltage of the slip will become Darker

However, one reason for using a parallel arrangement (or series-parallel combination) is that it allows a large number of LEDs to be combined with a safe supply voltage, and if you want to use a serial connection to achieve the same brightness, you may need a high Unacceptable voltage.

In the current competitive environment of the solar industry, PV module manufacturers are trying to make their products different, the main direction is to achieve the highest cost of the highest efficiency components. There are a lot of technical concepts and marketing programs have claimed that there are mature products, but most of the products can not stand a careful study of scrutiny. There are too many examples that some of the technical advantages achieved in a given way are not necessarily translated into the final proceeds of the component. For example, although the cost of the cell is reduced, the final cost of the component is not reduced; again, the efficiency of the cell may be improved, but the final component efficiency has not been improved to the same extent.